My down tube is 2" like your's Brad and as you know, I have a shift kit fitted and it all went together well. Also, my frame is 51cm, if anything it's smaller than your's. (You do need to fit a custom front engine mount, but aside from that, mine fitted like a dream.)

Nope, I don't think you have any worries there. (Check out the pics in my album here :- My Rides. My bike is almost the same as your's, by the sound of it. I just measured my seat tube - 27mm - same as your's too.)

Pity we don't live nearer to each other. I'm having a similar problem with Nigel, (will_start), in Wollongong. He needs a hand, but it's hard to get our heads together. (He has a clutch-related problem.)

Do check out the pics of my setup, they might help, and yell out if there's anything else I can do.